Overgrowing forest as a possible cause for the local extinction of Vipera aspis in the northern Swiss Jura mountains

In the northern Swiss Jura mountains, the Asp viper Vipera aspis was common until the 1940ies. During the past 50 years many local populations went extinct and nowadays the species is considered as threatened. We compared habitat characteristics of localities with extant viper populations with those of localities where the species became extinct. These two groups of localities did not differ in exposure, altitude, inclination, soil structure and cover of ground vegetation. However, localities where the species is still found were situated more frequently at forest edges, in dry meadows and at roadsides, whereas localities in which V. aspis became extinct were situated more frequently in forests. Tree density was lower at localities where the viper is still present. The results suggest that former habitats of V. aspis became overgrown by bushes and trees, which in turn may have led to a colder, more humid and thus unfavourable microclimate for V. aspis. We conclude that logging is an essential tool to maintain suitable habitat for this thermophilous ovoviviparous reptile.